In Switch-mode power converters (SMPC), current-mode pulse width-modulation (PWM) control and current-limited pulse-frequency-modulation (PFM) control schemes are widely used due to their fast dynamic response and automatic overcurrent protection. Both control schemes make use of the inductor current (e.g. of the Buck/Boost power stage) to modify the pulse width in PWM or oscillation frequency in PFM for voltage regulation. The inductor current is particularly important for PWM, as the signal sensed from the inductor current is combined with the artificial ramp signal in order to avoid sub harmonic oscillation in current-mode control PWM converters.
Regardless of the type of feedback control, almost all DC-DC converters and linear regulators sense the inductor current for overcurrent (overload) protection. Additionally, the sensed current is used in current-mode control DC-DC converters for loop control. Conventional current sensing methods insert a resistor in the path of the current to be sensed. However, this method incurs significant power losses, especially when the current to be sensed is high. Lossless current-sensing methods address this issue by sensing the current without dissipating the power using a passive resistor.
In the present document, a current sensing circuit is described which allows for a lossless sensing of the inductor current, i.e. of the current through the power switch of a DC-DC converter. The current sensing circuit described in the present document can be integrated on-chip, jointly with the DC-DC converter. Other applications of the current sensing circuit are e.g. fast switching, well controlled active current sources, amplifier/LDO (Low Dropout Regulator) overcurrent detection/protection circuits.